Web feeding apparatus

ABSTRACT

Web feeding apparatus comprising two pairs of web drive tractors, each pair drivable from a different one of two shafts, and an endless flexible belt by which the shafts are driven, the belt having a generally T-shape to engage the shafts at ends of the T-head and a drive wheel in the base of the T with a pair of idlers on either side of the T-stem and head junctions, in which the pair of idlers are moveable together in a curve transversely of the T-stem in the plane of the T. Such arcuate movement of the idlers with the drive wheel locked causes rephasing of the drive shafts and thus of the driven web.

United States Patent [191 Atkinson [11] 3,827,616 [451 Aug. 6, 1974 [73] Assignee: International Computers, Limited,

London, England 22 Filed: Mar. 12,1973 21 Appl. No.: 340,248

[30] Foreign Application Priority Data Mar. 14, 1972 Great Britain 11804/72 [52] US. Cl 226/74, 226/108, 226/188 [5 l] Int. Cl. G03b 1/30 {58] Field of Search 226/74, 75, 9, 188, 108

[56] References Cited UNITED STATES PATENTS 3,570,736 1/1969 Skiba 226/9 Primary Examiner-Allen N. Knowles Attorney, Agent, or Firm-Hane, Baxley & Spiecens 57 ABSTRACT Web feeding apparatus comprising two pairs of web drive tractors, each pair drivable from a different one of two shafts, and an endless flexible belt by which the shafts are driven, the belt having a generally T-shape to engage the shafts at ends of the T-head and a drive wheel in the base of the T with a pair of idlers on either side of the T-stem and head junctions, in which the pair of idlers are moveable together in a curve transversely of the T-stem in the plane of the T. Such arcuate movement of the idlers with the drive wheel locked causes rephasing of the drive shafts and thus of the driven web.

2 Claims, 5 Drawing Figures PATENTEDAUB 6l974 SHEET 1 BF 2 PAIENTED MIG 61974 3 82 7. 6 l 6 saw 2 BF z FIGS.

BACKGROUND OF THE INVENTION The invention relates to web feeding apparatus having means for adjusting the web in the direction of feed- High speed printers generally have two pairs of simultaneously drivable tractors one feeding into and the other feeding out of a printing position with the tractors of each pair being adjustable for engaging opposite edges, respectively, of a paper web to be driven. Normally, the tractors will advance the paper web by a pre set amount automatically between lines of print. This determines a particular line spacing. Sometimes, for example using preprinted fon'ns, it is desirable or necessary to line adjust the paper so that printing will be in the correct place. This adjustment is usually done by manually varying a drive to the tractors.

It is convenient for the tractor drive to comprise an endless belt or chain in a T configuration from a drive wheel at the base of the T to two driven shafts, one at each end of the cross-piece of the T and each driving a different pair of tractors. The general T-shape of the belt or chain is achieved by using idler rollers. If these idler rollers are capable of movement together and parallel to the T cross-piece line adjustment of the web will be achieved with the drive wheel locked against rotation. Unfortunately, however, this tends to require either different belt or chain lengths or additional idle rollers. Any requirement for extensibility of a drive belt is in direct contradiction to the requirement for synchronised movement of the two driven shafts by the drive belt. Also, it is desirable to keep idler roller arrangements as simple as possible.

SUMMARY OF THE INVENTION According to the invention web feeding apparatus comprises two pairs of web drive tractors each pair drivable from a different one of two shafts, an endless flexible drive member in a generally T-configuration engaging the shafts at ends of the T-head, a drive wheel in the base of the T, and a pair of idlers on either side of the T-stem at its junction with the T-head, the pair of idlers being movable together in a curve transversely of the T-stem in the plane of the T.

Preferably, a support for the pair of idlers is pivoted about the same axis as the drive wheel is rotatable. Also, when pivoted to align its centre with the drive wheel and the nearest of the shafts, each idler wheel should be spaced from that shaft only by an amount substantially equal to the thickness of the drive member.

An arcuate movement of the idlers substantially reduces differences of length requirements for the drive member. It is particularly convenient for the idlers to be mounted on a support pivotable about an axis chosen to minimise stretching of the drive member over the required range of adjustment.

BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the invention will now be particularly described with reference to the drawings, in which:

FIG. 1 shows, diagrammatically, a tractor arrangement of a high speed printer;

FIG. 2 shows details of a tractor drive arrangement embodying the invention;

FIG. 3 is a section on the line A A of FIG. 2;

FIG. 4 is useful in showing the differences of drive belt length required by a prior proposal; and

FIG. 5 is useful in showing how an embodiment of this invention improves on the FIG. 4 proposal.

PREFERRED EMBODIMENT In FIG. 1, two pairs of paper tractors are shown one v above and the other below a printing position. The

upper and lower pairs of tractors are identically arranged. The upper pair of tractors 10 and 11 feed paper out of the printing position. Each tractor has pins 12 extending through a slot to engage perforations near opposite edges of paper to be fed. In conventional manner, the pins 12 of each tractor are on an endless tractor band, preferably a notched belt, carried by cooperating pulleys or sprockets at least one of which is keyed and driven by a splined shaft. There are two splined shafts 14 one for each pair of tractors, with smooth shafts shown at 15 for the other pulleys to rotate freely.

The tractor band shafts l4 and 15 are rotatable in the machine frame at 16 and 17. The splined shafts 14 are shown extending through the machine frame at 16 to a drive and adjustment mechanism embodying this invention and indicated generally at 20.

Each tractor is mounted on a positioning member, shown as 18 and 19 for the upper tractors 10 and 11, respectively. The tractors are slidable along the tractor band shafts 14 and '15, and the positioning members serve in locating each pair of tractors laterally of the web and establishing the tractor spacing for particular paper widths. A suitable arrangement for accomplishing this would operate on the extensions of the positioning members through the machine frame at 17 and could be constructed as disclosed in our copending US. Pat. application No. 8,235/7l.

The drive and adjustment mechanism 20 is shown in greater detail in FIGS. 2 and 3. The splined tractor band drive shafts 14 are shown engaged directly by a toothed belt 21 that is maintained in a generally T- configuration by a pair of idle guide rollers 22, 23 and its engagement with a toothed drive wheel 24. The drive shafts 14 are at opposite ends of the T-head with the drive wheel 24 at the base of the T-stem and the idlers 22, 23 at the junctions of T-head and stem.

The drive wheel 24 is keyed to a shaft 25 driven by an electric clutch and brake unit 26 through any convenient linkage. This will cause both pairs of tractors to feed paper simultaneously when the shaft 25 is rotated. Normally, the shaft 25 is indexed in amounts appropriate to a desired line spacing of printing on the paper, and is braked between such indexing movements. When using lined or preprinted forms it may be necessary or desirable to adjust the position of the paper prior to printing one or more lines. This is achieved with the present embodiment by moving the idler rollers 22 and 23 bodily in a generally arcuate manner which will, with the drive wheel 24 locked against rotation, achieve a desired rotational adjustment of the tractor band drive shafts 14.

To this end, the idler rollers 22 and 23 are freely rotatable on shafts 27 and 28, respectively, fixed on a support member 29 which is itself pivotable to produce desired arcuate movement of the idlers 22 and 23. The

idler support 29 is pivoted about the same axis as the drive wheel 24, and, in the middle setting shown, the idlers extend beyond positions for which the drive belt returns parallel to the plane of the driven shaft axes so as to minimise distension of the belt 21 over the required range of adjustment. As best seen in FIG. 3, the idler support 29 is mounted on a shaft 30. The support 29 is preferably keyed to the shaft 30 which is rotatable in the machine frame at 16 and is normally locked in any particular position by any suitable means, such as a normally energised magnetic clutch 31.

The idler support 29 is pivotable only when the shaft 25 is braked. This may be done manually using a lever 32 secured to the support 29 and it will be convenient for there to be a micro switch on or associated with the lever 32 for releasing the lock on the shaft 30, say by interrupting energisation of the clutch 31.

The way in which a prior proposal for rephasing the tractor band drive shafts results in varying drive belt length requirements is demonstrated in FIG. 4. There the arrow X shows the direction of rectilinear movement of the idler rollers together and parallel with the T-head so that their centres each move a distance z along that direction X. With the drive wheel locked against rotation, this will result in a length z of the drive belt being pulled round one or the other of the tractor drive shafts to move both of the latter through a corresponding angle. The direction of rotation of the drive shafts will depend on the direction of movement of the idler rollers, a counter clockwise direction being shown in FIG. 4 for a downward movement of the idlers. The shift of the tangent points of the belt with the drive wheel are clearly equal and opposite and those at the idlers also tend to cancel each other being on opposite sides of the directional arrow X. However, there will be a requirement for a greater total belt length between the idlers and the drive wheel due to the approximate proportionality with a hypotenuse rather than one side of a right angled triangle.

Corresponding actions using an embodiment of the invention will be evident from FIG. 5 where it will be seen that the idlers are moved along an arc Y between extreme positions, shown dotted for the upper idler, at which one or the other idler, save for the drive belt thickness, contacts the respective drive shaft periphery when their centres align with the drive wheel axis. The arcuate movement results in one idler moving relatively towards one T-head and stem intersection and other moving relatively away from the other T-head and stem intersection in a roughly complementary way. The change of tangent points on the drive wheel will be similar to that for FIG. 4, but the total belt length between the tangent points of the idlers and drive wheel will be substantially constant being related to radius rather than to different sides of right angled triangle. In fact, the only length difference requirement will arise from the chords from the driven shafts to the idlers and this will be small. Embodiments of the invention are thus able to very much reduce stretching requirements for the drive belt.

I claim:

1. Web feeding apparatus comprising two pairs of web drive tractors; two drive shafts each for driving a different pair of tractors; a drive wheel; an endless flexible belt engaging both drive shafts and the drive wheel; a pair of idlers also engaging the flexible belt to make a substantially T-configuration of the belt with drive shafts at the end of the T-stem; a pivotted support means for the idlers, the support means being pivotable about the same axis as the drive wheel so that the idlers are movable through a curve transversely of the T-stem in the plane of the T.

2. Apparatus according to claim 1, wherein, in the direction of the stem, the idlers are ahead of true right angled junctions of the T-head and stem, and either idler would be spaced from its nearest shaft by the thickness of the'belt if the support means was pivoted to align the centre of that idler with those of the drive wheel and that nearest shaft. 

1. Web feeding apparatus comprising two pairs of web drive tractors; two drive shafts each for driving a different pair of tractors; a drive wheel; an endless flexible belt engaging both drive shafts and the drive wheel; a pair of idlers also engaging the flexible belt to make a substantially T-configuration of the belt with drive shafts at the end of the T-stem; a pivotted support means for the idlers, the support means being pivotable about the same axis as the drive wheel so that the idlers are movable through a curve transversely of the T-stem in the plane of the T.
 2. Apparatus according to claim 1, wherein, in the direction of the stem, the idlers are ahead of true right angled junctions of the T-head and stem, and either idler would be spaced from its nearest shaft by the thickness of the belt if the support means was pivoted to align the centre of that idler with those of the drive wheel and that nearest shaft. 